The outbreak of E. coli O121 was first detected by health officials last week. Samples of frozen chicken mini-quesadillas produced by Rich Products tested positive for the strain of E. coli at the New York State Department of Health Wadsworth Laboratory, according to the Department of Agriculture's Food Safety Inspection Service.

Eight of the people who fell ill, in Michigan, Mississippi, New York, Ohio, Pennsylvania, Texas and Virginia, told investigators they ate products from the firm, the USDA said in a release.

The company posted a notice on its website saying, "Consumer safety is our number one priority, and we are voluntarily recalling these products effective immediately."

The company said, "Each of our product packages contain cooking instructions on the back of the packaging that, if followed, will effectively destroy any E.Coli bacteria. These preparation instructions have been validated following the Grocery Manufacturers Association industry protocol to ensure food safety."

Food safety experts said consumers shouldn't have to presume the food is contaminated. "These are frozen products that need to be cooked, but they should not have E. coli in them, because most of the ingredients should have been processed beforehand," said Douglas Powell, a professor of food safety at Kansas State University in Manhattan, Kan.

The recalled products include:

7.2-oz. cartons of Farm Rich mini-pizza slices with cheese, pepperoni and sauce in pizza dough, UPC code 041322376909 with a best-by date of May 15 or May 16, 2014.

22-oz. cartons of Farm Rich mini-pizza slices with cheese, pepperoni and sauce in pizza dough, UPC code 041322356437 with a best-by date of May 15 or May 16, 2014.

22-oz. cartons of Farm Rich mozzarella bites in a pizzeria style crust, UPC code 041322374431 with a best-by date of May 19, 2014.

7-oz. cartons of Farm Rich mozzarella bites in a pizzeria style crust, UPC code 041322376916 with a best-by date of May 19, 2014.

22-oz. bags of Market Day Mozzarella Bites, UPC code 041322804358 with a best-by date of May 12, 2014.

Although the foods were produced Nov. 12-19, 2012, the Department of Agriculture is concerned some consumers could still have them in their freezers.

Consumers with more questions can contact the company's consumer line at (888) 220-5955 from 8 a.m. to 8 p.m. ET Monday through Friday or visit the company website at www.farmrich.com.

The E. coli strain in the outbreak, O121, is rarer — "but becoming less so with better testing" — than the more common O157:H7 found in multiple hamburger outbreaks over the years, Powell said.

Infection with E. coli O121 can result in dehydration, bloody diarrhea and abdominal cramps for three to four days on average. Most people recover within a week, but some go on to develop a type of kidney failure called Hemolytic Uremic Syndrome. It is most common in children under 5 and older adults. Symptoms include fever, abdominal pain, pale skin tone, fatigue, small, unexplained bruises or bleeding from the nose and mouth, decreased urination and swelling. People who experience these symptoms should seek emergency medical care immediately.